It is commonly necessary to cast anchor bolts into concrete structures such as pile caps, equipment bases, and walls, for purposes of anchoring fixtures ranging from structural steel columns and heavy equipment for commercial and industrial buildings and other large structures, to wooden sill plates on residential foundation walls. Anchor bolts may be required to resist a variety of loads, such as uplift forces, out-of-plane lateral loads, and in-plane shear loads. In cases where anchor bolts by themselves would not provide the required load resistance, steel straps or plates or other appurtenances may need to be used in conjunction with the anchor bolts to transfer loads to the concrete structure.
Regardless of the specific purpose of the anchor bolts, it is always desirable and often critically important to ensure that the anchor bolts are held securely in position during construction, so that after the concrete has cured, the anchor bolts will be properly positioned and aligned to receive the fixtures they are intended to anchor. This entails positioning the anchor bolts accurately and securely in the formwork such that they are not susceptible to being knocked out of lateral position or angular alignment during placement of concrete in the formwork, and during related operations such as vibration of the freshly-placed concrete. Misplacement or misalignment of anchor bolts can result in the need for costly and time-consuming modifications to the concrete elements in which they have been cast and/or to the fixtures that they are intended to anchor.
There are many known methods and means for positioning anchor bolts in formwork. One simple and common method is to use anchor bolt templates made from dimension lumber (e.g., 2×6s, 2×8s, etc.) or plywood. In cases where multiple anchor bolts are required for anchoring a single fixture (such as the base plate for a structural column), the appropriate bolt pattern is marked out on the wooden template, and slightly oversize holes are drilled in the template to receive the anchor bolts. The bolts are then inserted into the holes in the templates, typically along with nuts and washers or other means to set the height that the bolts will project above the finished concrete. The assembly of the wooden template and anchor bolts is temporarily secured to the formwork, and then concrete can be placed in the formwork. In cases where individual anchor bolts are required at intermittent intervals, such as for anchoring a wooden sill plate to the top of a residential foundation wall (for supporting a wood-framed floor structure), the bolts can be positioned in holes in individual wooden templates temporarily secured to the wall forms.
These methods are satisfactory if carried out with proper care. Unfortunately, however, that often does not happen, and the result is anchor bolts that have been cast into the concrete in the wrong position in one or both lateral directions, and/or out of angular alignment, due to factors such as inaccurate marking and drilling of bolt-receiving holes in the wooden templates, and inaccurate or insufficiently secure positioning of the templates on the formwork.
Various types of anchor bolt positioning devices are commercially available, but they can be expensive or comparatively difficult to use. Accordingly, there is a need for anchor bolt positioning apparatus that is inexpensive and simple to use, while reducing the chances of error with respect to the positions of anchor bolts in finished concrete structures.